This invention relates to surgically implantable prosthetic devices and more particularly such devices for the replacement of non-weight bearing joints.
While the invention finds particular use as a replacement for a dysfunctional wrist joint and will be described in the context, it will be appreciated by those skilled in the art that the invention has broader applications and is applicable to other joints. Such joints include, for example, the metacarpophalangeal, thumb carpometarcarpal, radiohumeral and glenohumeral articulations.
Currently, there are devices available for either total or partial replacement of the knuckle, wrist, elbow, shoulder, hip, knee and ankle joints. These devices use one or more of the possible types of mechanical articulations available; that is, hinge, ball and socket, or runners in grooves. Most devices use intramedullary stems and acrylic bone cement to secure the prosthesis to bone. Presently available prostheses have components constructed from several types of biologically inactive metals and designed to articulate with other components constructed from a plastic, such as high density polyethylene.
Several methods or techniques are used to insure that the components remain articulated, and these methods include the use of the soft tissues existent at the time of implantation, the use of pins or screws to hold articular surfaces together and the use of bayonet type locks. Some types of the available prostheses are quite simple while other types comprise complex mechanical systems, with both types having attendant or inherent disadvantages. The principal disadvantage of the simple prosthesis is that they may not reproduce the full range of motion of the joint. The principal disadvantage of the complex prosthesis is due to the potential complexities of surgery and increased chance of failure. Typical causes of such failure include fracture of bone during reaming and breakage of the implant itself. Additionally, the prosthesis components, such as pins, screws or intramedullary stems work loose following implantation. In the event of failure, fusion may be required, but such surgery may be difficult if a great deal of bone has been removed.